U.S. patent application number 12/310149 was filed with the patent office on 2009-10-01 for charged particle beam apparatus and method adjusting axis of aperture.
Invention is credited to Hiroshi Matsumura, Takashi Ogawa, Yo Yamamoto.
Application Number | 20090242757 12/310149 |
Document ID | / |
Family ID | 39106646 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090242757 |
Kind Code |
A1 |
Ogawa; Takashi ; et
al. |
October 1, 2009 |
CHARGED PARTICLE BEAM APPARATUS AND METHOD ADJUSTING AXIS OF
APERTURE
Abstract
There are provided a charged particle beam apparatus and a
method of adjusting an axis of an aperture capable of adjusting a
position of a center axis of the aperture easily and accurately in
a short period of time. A charged particle beam apparatus 1
includes a charged particle source 9, an aperture 18, an object
lens 12, observing means 32, an aperture driving portion 19, and a
control portion 30. The control portion 30 includes spot pattern
forming means 33 for forming a plurality of spot patterns on a
surface N1 of a sample N by irradiating a charged particle beam I,
analyzing means for calculating a position of a spot center of the
spot pattern and a geometrical center position of a halo, and
adjusting position determining means 35 for calculating an
adjusting position based on a position of intersecting lines of
connecting the positions of the spot centers of the respective spot
patterns and the center position of the halo, in which a position
of the aperture 18 is adjusted by moving the center axis of the
aperture 18 to the adjusting position.
Inventors: |
Ogawa; Takashi; (Chiba,
JP) ; Yamamoto; Yo; (Chiba, JP) ; Matsumura;
Hiroshi; (Chiba, JP) |
Correspondence
Address: |
Bruce L Adams;Adam & Wilks
17 Battery Place, Suite 1231
New York
NY
10004
US
|
Family ID: |
39106646 |
Appl. No.: |
12/310149 |
Filed: |
August 3, 2007 |
PCT Filed: |
August 3, 2007 |
PCT NO: |
PCT/JP2007/065237 |
371 Date: |
April 24, 2009 |
Current U.S.
Class: |
250/306 ;
250/396R |
Current CPC
Class: |
H01J 37/28 20130101;
H01J 2237/024 20130101; H01J 37/20 20130101; H01J 37/09 20130101;
H01J 2237/0458 20130101; H01J 37/15 20130101; H01J 37/3056
20130101 |
Class at
Publication: |
250/306 ;
250/396.R |
International
Class: |
G01N 23/00 20060101
G01N023/00; H01J 3/14 20060101 H01J003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2006 |
JP |
2006-226867 |
Claims
1. A charged particle beam apparatus characterized by comprising: a
charged particle source of emitting a charged particle beam; an
aperture of narrowing the charged particle beam to a predetermined
diameter; an object lens of focusing the charged particle beam
narrowed by the aperture to irradiate to a sample; observing means
capable of acquiring an image of a surface of the sample; an
aperture driving portion capable of moving a center axis of the
aperture in an X direction and a Y direction constituting two axes
substantially orthogonal to each other relative to the center axis;
and a control portion capable of adjusting a position of the center
axis of the aperture relative to a center axis of the object lens
by moving the aperture by the aperture driving portion; wherein the
control portion includes: spot pattern forming means of forming a
plurality of spot patterns on the surface of the sample by
irradiating the charged particle beam to the sample by a plurality
of times by moving the aperture to a position different in the X
direction and the Y direction by the aperture driving portion;
analyzing means for calculating positions of spot centers
constituting centers of the respective spot patterns formed at the
sample and a geometrical center position of a halo constituting an
outer edge thereof from the image acquired by the observing means;
and adjusting position determining means for calculating an
adjusting position of the center axis of the aperture based on a
position of intersecting lines of connecting the positions of the
spot centers of the respective spot patterns and the center
position of the halo calculated by the analyzing means; and wherein
a position of the aperture is adjusted by moving the center axis of
the aperture to the adjusting position calculated by the adjusting
position determining means.
2. The charged particle beam apparatus according to claim 1,
characterized by further comprising: scanning means capable of
moving a position of irradiating the charged particle beam relative
to the sample; wherein the spot pattern forming means of the
control portion moves the position of irradiating the charged
particle beam relative to the sample by the scanning means by
amounts of amounts of moving the aperture respectively in the X
direction and the Y direction multiplied by a constant value at
every time of irradiating the charged particle beam to the sample
by moving the center axis of the aperture.
3-4. (canceled)
5. A method of adjusting an axis of an aperture relative to a
center axis of an object lens with regard to a charged particle
beam apparatus of narrowing a charged particle beam emitted from a
charged particle source to a predetermined diameter by the aperture
and focusing the charged particle beam by the object lens to be
irradiated to a sample, the method characterized by comprising: a
spot pattern forming step of forming a plurality of spot patterns
on a surface of the sample by making the position of the center
axis of the aperture differ in an X direction and a Y direction
constituting to two axes substantially orthogonal to the center
axis and irradiating the charged particle beam to the previously
prepared sample by a plurality of times; a spot analyzing step of
calculating positions of spot centers constituting centers of the
respective spot patterns and a geometrical center position of a
halo constituting an outer edge thereof; an adjusting position
determining step of calculating an adjusting position of the center
axis of the aperture based on positions of intersecting lines
connecting the center positions of the halos of the respective spot
patterns and the position of the spot center; and a center axis
position adjusting step of moving the center axis of the aperture
to the calculated adjusting position.
6. The method of adjusting an axis of an aperture according to
claim 5, characterized in that at the spot pattern forming step, a
position of irradiating the charged particle beam is moved relative
to the sample by amounts of respective moving amounts in the X
direction and the Y direction of the aperture multiplied by a
constant value at every time of irradiating the charged particle
beam to the sample by moving the center axis of the aperture.
7-8. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a charged particle beam
apparatus of working, observing a sample by irradiating a charged
particle beam to the sample and a method of adjusting an axis of an
aperture of a charged particle beam apparatus.
BACKGROUND ART
[0002] In a background art, a charged particle. beam apparatus of
carrying out working, observation or the like by irradiating a
charged particle beam of an ion beam, an electron beam or the like
to a predetermined position has been used in various fields. As a
charged particle beam apparatus, there is, for example, a scanning
electron microscope (SEM) capable of irradiating an electron beam
as a charged particle beam, or a focused ion beam apparatus (FIB)
capable of irradiating a focused ion beam as a charged particle
beam or the like. According to a scanning electron microscope, a
state of a surface of the sample can be observed by detecting a
secondary electron generated from the surface of the sample while
scanning an electron beam on the surface of the sample. Further,
according to the focused ion beam. apparatus, the surface of the
sample can be observed by detecting a secondary electron similar to
a scanning electron microscope, etching or deposition of a sample
can be carried out by making an acceleration voltage high, and the
focused ion beam apparatus is used for forming a sample of TEM
(transmission electron microscope), correcting a photomask or the
like. Further, in recent years, in a focused ion beam apparatus,
attention is paid to a method of realizing a low damage working by
using the focused ion beam apparatus in a low acceleration region
of setting an acceleration voltage of a focused ion beam to about
100 V through 5000 V. Further, attention is also paid to a method
of realizing a large area working of wire bonding, solder bump or
the like by using a focused ion beam apparatus within a range of an
acceleration voltage of about 3000 V in a large current region of
constituting an amount of irradiating a focused ion beam to be
equal to or higher than 1 nA.
[0003] Meanwhile, according to the charged particle beam apparatus,
in order to carry out accurate observation or working, it is
necessary to remove dimming referred to as off-axis aberration in
accordance with adjusting a focal point position. An off-axis
aberration is generated by that a center of a charged particle beam
does not pass a center axis of an object lens, further
specifically, caused by that a deviation is brought about between a
center axis of an aperture of narrowing a charged particle beam to
be incident on an object lens and a center axis of the object lens.
Therefore, in order to carry out accurate observation or working by
removing an off-axis aberration, it is necessary to adjust a
position of the center axis of the aperture to coincide with the
center axis of the object lens before being used.
[0004] In a background art, such an off-axis aberration has been
removed specifically by the following method. That is, a center
axis of an aperture is made to be disposed at an arbitrary
position, and an image in a state of over focal point and an image
in a state of under focal point are alternately acquired by
adjusting a focal point position of the object lens. In a state in
which the center axis of the aperture and the center of the object
lens do not substantially coincide with each other, a position of
the image described in the state of the over focal point and a
position of the image described in the state of under focal point
differ from each other, and therefore, when the focal point
position of the object lens is changed, the acquired image is much
changed. Further, the center axis of the aperture and the center
axis of the object lens are made to coincide with each other by
making the position of the image remain unchanged even when the
focal point position is changed by repeating the above-described
operation while adjusting the center axis of the aperture (refer
to, for example, Nonpatent Reference 1).
[0005] Further, as other method, respectively in a state of over
focal point and a state of under focal point, a charged particle
beam is scanned on a knife edge, and an error of a current value
detected by the knife edge by the state of over focal point and the
state of under focal point is calculated. Further, a method of
repeatedly changing to adjust a position of an aperture until the
error of the current value falls in a predetermined range has been
proposed (refer to, for example, Patent Reference 1).
Nonpatent Reference 1: "Basic and Application of Scanning Electron
Microscope", Kyoritsu Shuppan K. K. Oct. 25, 1991, p. 78-79
Patent Reference 1: JP-A-2005-276639
DISCLOSURE OF THE INVENTION
[0006] Problems that the Invention is to Solve
[0007] However, in the method according to Nonpatent Reference 1, a
deviation of the center axis of the aperture is grasped only
qualitatively from a change between the image in the over focal
point state and the image in the under focal point state, and
therefore, the adjustment of the center axis of the aperture can be
realized by repeatedly carrying out the adjustment by manual
operation based on the above-described phenomenon and an empirical
rule. Therefore, in adjusting the center axis of the aperture,
there poses a problem that technique of an operator and enormous
time are needed. Particularly, when used in a large current region
as described above, a working speed is fast, and therefore, a
method of carrying out an adjusting operation swiftly to minimize
damage of the sample is desired. Further, an adjusting accuracy is
dispersed among respective operators, further, even when adjusted
by the same operator, it is difficult to unify the adjusting
accuracy among different apparatus, and a problem of bringing about
a dispersion in a performance among apparatus is posed. Further,
when the charged particle beam is irradiated in a low acceleration
region as described above, the aberration of the charged particle
beam is enlarged and dimming is brought about also owing to the
fact that the acceleration voltage is a low voltage. Therefore, an
aberration caused by the deviation of the center axis of the
aperture and an aberration caused by the acceleration voltage
cannot be separated from each other, and a problem that the center
axis of the aperture cannot accurately be adjusted is posed.
[0008] Further, although in the method according to Patent
Reference 1, the deviation of the aperture can be evaluated and
adjusted quantitatively to some degree by the error of the current
value and a correlative relationship between the error of the
current value and the deviation of the aperture is not clear, and
the deviation needs to be adjusted by repeatedly carrying out the
adjusting operation. Therefore, similar to Nonpatent Reference 1, a
problem of needing enormous time in adjustment is posed.
[0009] The invention has been carried out in view of the
above-described situation and provides a charged particle beam
apparatus and a method of adjusting an axis of an aperture capable
of adjusting a position of a center axis of an aperture in a short
period of time, easily and accurately.
Means for Solving the Problems
[0010] In order to resolve the above-described problem, the
invention proposes the following means.
[0011] A charged particle beam apparatus of the invention is
characterized by including a charged particle source of emitting a
charged particle beam, an aperture of narrowing the charged
particle beam to a predetermined diameter, an object lens of
focusing the charged particle beam narrowed by the aperture to
irradiate to a sample, observing means capable of acquiring an
image of a surface of the sample, an aperture driving portion
capable of moving a center axis of the aperture in an X direction
and a Y direction constituting two axes substantially orthogonal to
each other relative to the center axis, and a control portion
capable of adjusting a position of the center axis of the aperture
relative to a center axis of the object lens by moving the aperture
by the aperture driving portion, wherein the control portion
includes spot pattern forming means of forming a plurality of spot
patterns on the surface of the sample by irradiating the charged
particle beam to the sample by a plurality of times by moving the
aperture to a position different in the X direction and the Y
direction by the aperture driving portion, analyzing means for
calculating positions of spot centers constituting centers of the
respective spot patterns formed at the sample and a geometrical
center position of a halo constituting an outer edge thereof from
the image acquired by the observing means, and adjusting position
determining means for calculating an adjusting position of the
center axis of the aperture based on a position of intersecting
lines of connecting the positions of the spot centers of the
respective spot patterns and the center position of the halo
calculated by the analyzing means, and wherein a position of the
aperture is adjusted by moving the center axis of the aperture to
the adjusting position calculated by the adjusting position
determining means.
[0012] Further, the invention is directed to a method of adjusting
an axis of an aperture of adjusting a position of a center axis of
an aperture relative to a center axis of an object lens with regard
to a charged particle beam apparatus of narrowing a charged
particle beam emitted from a charged particle source to a
predetermined diameter by the aperture and focusing the charged
particle beam by the object lens to be irradiated to a sample, the
method is characterized by including a spot pattern forming step of
forming a plurality of spot patterns on a surface of the sample by
making the position of the center axis of the aperture differ in an
X direction and a Y direction constituting to two axes
substantially orthogonal to the center axis and irradiating the
charged particle beam to the previously prepared sample by a
plurality of times, a spot analyzing step of calculating positions
of spot centers constituting centers of the respective spot
patterns and a geometrical center position of a halo constituting
an outer edge thereof, an adjusting position determining step of
calculating an adjusting position of the center axis of the
aperture based on positions of intersecting lines connecting the
center positions of the halos of the respective spot patterns and
the position of the spot center, and a center axis position
adjusting step of moving the center axis of the aperture to the
calculated adjusting position.
[0013] According to the charged particle beam apparatus and the
method of adjusting the axis of the aperture according to the
invention, as the spot pattern forming step, the plurality of spot
patterns are formed on the surface of the sample. That is, the spot
pattern forming means of the control portion irradiates the charged
particle beam to an arbitrary position of the surface of the sample
by emitting the charged particle beam from the charged particle
source. Thereby, at the arbitrary position of the surface of the
sample, the spot pattern of a predetermined size is formed in
accordance with a focal point state of the irradiated charged
particle beam. Next, the spot pattern forming means of the control
portion forms the spot pattern by moving the center axis of the
aperture in the X direction and the Y direction by the
predetermined moving amounts by the aperture driving portion and
irradiating again the charged particle beam. Each of the plurality
of spot patterns formed in this way shows a shape having the spot
center constituting the center and the halo constituting the outer
edge. The halo shows a range of irradiating the charged particle
beam on the surface of the sample. Further, when the center axis of
the aperture is positionally shifted relative to the center axis of
the object lens, the spot center is formed at a position eccentric
in the direction in correspondence with the direction of the
positional shift of the center axis of the aperture relative to the
geometrical center position of the halo.
[0014] Next, as the spot pattern analyzing step, the formed spot
pattern is analyzed. That is, the analyzing means of the control
portion calculates the positions of the spot centers of the
respective spot patterns and the position of the geometrical center
of the halo described in the image of the surface of the sample
acquired by the observing means. Next, as the adjusting position
determining step, the adjusting position of the center axis of the
aperture at which the center axis of the aperture and the center
axis of the object lens substantially coincides with each other is
determined. That is, the adjusting position determining means of
the control portion calculates the position of intersecting the
lines of connecting the positions of the spot centers of the
respective spot patterns and the center position of the halo as the
adjusting position from a result of the spot pattern analyzing
step. Finally, as the center axis position adjusting step, the
control portion can bring about the state in which the center axis
of the aperture substantially coincide with center axis of the
object lens by moving the center axis of the aperture to the
calculated adjusting position by the aperture driving portion.
[0015] Further, it is made to be further preferable that the
above-described charged particle beam apparatus further includes
scanning means capable of moving a position of irradiating the
charged particle beam relative to the sample, wherein the spot
pattern forming means of the control portion moves the position of
irradiating the charged particle beam relative to the sample by the
scanning means by amounts of amounts of moving the aperture
respectively in the X direction and the Y direction multiplied by a
constant value at every time of irradiating the charged particle
beam to the sample by moving the center axis of the aperture.
[0016] Further, it is made to further preferable in the
above-described method of adjusting the axis of the aperture that
at the spot pattern forming step, a position of irradiating the
charged particle beam is moved relative to the sample by amounts of
respective moving amounts in the X direction and the Y direction of
the aperture multiplied by a constant value at every time of
irradiating the charged particle beam to the sample by moving the
center axis of the aperture.
[0017] According to the charged particle beam apparatus and the
method of adjusting the axis of the aperture according to the
invention, when the plurality of spot patterns are formed at the
spot pattern forming step, the center axis of the aperture is made
to be disposed at the position which differs in the X direction and
the Y direction, and the position of irradiating the charged
particle beam is moved relative to the sample by the scanning
means. Therefore, the plurality of spot patterns can be formed not
to overlap each other on the surface of the sample, the image
capable of further clearly identifying the spot pattern can be
acquired, and the axis can be adjusted further accurately. At this
occasion, by constituting the relative moving amount of the
position of irradiating the charged particle beam by the amounts of
the amounts of moving the center axis of the aperture in the X
direction and the Y direction multiplied by the constant value, the
moving direction can be made to coincide with the direction of
positionally shifting the center axis of the aperture relative to
the center axis of the object lens. Therefore, even when the
position of irradiating is relatively moved as described above, at
a search position determining step, the search position can be
determined similarly based on the position of intersecting the
lines of connecting the positions of the spot centers and the
center position of the halo.
[0018] Further, it is made to be further preferable in the
above-described charged particle beam apparatus that the control
portion sets the charged particle beam to the sample in a state of
an over focal point when the charged particle beam is irradiated to
the sample by the spot pattern forming means.
[0019] Further, it is made to be further preferable in the
above-described method of adjusting the axis of the aperture that
at the spot pattern forming step the charged particle beam focused
by the object lens is irradiated to the sample in a state of an
over focal point.
[0020] According to the charged particle beam apparatus and the
method of adjusting the axis of the aperture according to the
invention, at the spot pattern forming step, by setting the charged
particle beam in the state of the over focal point by the spot
pattern forming means of the control portion to irradiate to the
sample, in comparison with a state of an under focal point, the
formed spot pattern can be formed to be larger. Therefore, at the
spot pattern analyzing step, the spot pattern can further clearly
be identified from the acquired image and a further accurate axis
adjustment can be carried out.
[0021] Further, it is made to be further preferable in the
above-described charged particle beam apparatus that the analyzing
means of the control portion constitutes a binarized data
constituted by processing to binarize the image acquired from the
observing means and calculates the center position of the halo and
the position of the spot center of the spot pattern based on the
binarized data.
[0022] Further, it is made to be further preferable in the
above-described method of adjusting the axis of the aperture that
at the spot pattern analyzing step, a binarized data of processing
to binarize the image of the surface of the sample formed with the
spot pattern is formed, and the center positions of the halos of
the respective spot patterns and the position of the spot center
are calculated from the binarized data.
[0023] According to the charged particle beam apparatus and the
method of adjusting the axis of the aperture according to the
invention, at the spot pattern analyzing step, by constituting the
binarized data of processing to binarize the image by the analyzing
means of the control portion, the spot pattern displayed on the
image can further clearly be identified and the further accurate
axis adjustment can be carried out.
ADVANTAGE OF THE INVENTION
[0024] According to the charged particle beam apparatus of the
invention, by only providing the spot pattern forming means, the
analyzing means, the adjusting position determining means as the
control portion and forming the plurality of spot patterns at the
sample, the position of the center axis of the aperture can be
adjusted automatically, easily and accurately in the short period
of time.
[0025] Further, according to the method of adjusting the axis of
the aperture of the invention, by only providing the spot pattern
forming step, the spot pattern analyzing step, the adjusting
position determining step, and forming the plurality of spot
patterns to the sample, the position of the center axis of the
aperture can be adjusted easily and accurately in the short period
of time and automation is applicable thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a constitution view of a charged particle beam
apparatus according to a first embodiment of the invention.
[0027] FIG. 2 is a flowchart of adjusting an axis of an aperture
according to the first embodiment of the invention.
[0028] FIG. 3 is an explanatory diagram showing a relationship
between a center axis of an aperture and a center axis of an object
lens according to the first embodiment of the invention.
[0029] FIG. 4 illustrates detailed views of a spot pattern formed
at a spot pattern forming step according to the first embodiment of
the invention.
[0030] FIG. 5 is a plane view showing an image of a surface of a
standard sample formed with the spot pattern according to the first
embodiment of the invention.
[0031] FIG. 6 is an explanatory diagram showing a relationship
between the center axis of the aperture at a first portion and a
center axis of the aperture at a second portion according to the
first embodiment of the invention.
[0032] FIG. 7 is a plane view showing an image of a surface of a
standard sample formed with a spot pattern according to a modified
example of the first embodiment of the invention.
[0033] FIG. 8 is a constitution view of a charged particle beam
apparatus according to a second embodiment of the invention.
[0034] FIG. 9 is a constitution view of a charged particle beam
apparatus according to a third embodiment of the invention.
[0035] FIG. 10 is a constitution view of a charged particle beam
apparatus according to a fourth embodiment of the invention.
[0036] FIG. 11 is a detailed view of a spot pattern formed at a
spot pattern forming step of the fourth embodiment of the
invention.
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
[0037] 1 focused ion beam apparatus (charged particle beam
apparatus) [0038] 9 ion source (charged particle source) [0039] 12
object lens [0040] L12 center of object lens [0041] 18 scanning
electrode (scanning means) aperture [0042] L18 center axis of
aperture [0043] 19 aperture driving portion [0044] 30 control
portion [0045] 32 observing means [0046] 33 spot pattern forming
means [0047] 34 analyzing means [0048] 35 adjusting position
determining means [0049] I ion beam (charged particle beam) [0050]
M sample [0051] N standard sample (sample) [0052] N1 surface [0053]
P, Q, O, R, P' spot patterns [0054] P1, Q1, O1, R1 halos [0055] P2,
Q2, O2, R2 spot centers [0056] P3, Q3, O3, R3 centers of halos
[0057] S2 spot pattern forming step [0058] S4 spot pattern
analyzing step [0059] S5 adjusting position determining step [0060]
S6 center axis position adjusting step
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
[0061] FIG. 1 shows a first embodiment according to the invention.
As shown by FIG. 1, a focused ion beam apparatus (FIB) 1
constituting a charged particle beam apparatus carries out working
of a surface of a sample M or the like by irradiating an ion beam I
constituting a charged particle beam to the sample M. For example,
a sample for observation by TEM (transmission electron microscope)
can be fabricated by arranging, for example, a wafer as the sample
M, or a photomask can be corrected or the like by constituting a
photomask in photolithography technology as the sample M. Details
of the focused ion beam apparatus 1 according to the embodiment
will be explained as follows.
[0062] As shown by FIG. 1, the focused ion beam apparatus 1
includes a sample base 2 capable of arranging the sample M, and an
ion beam lens-barrel 3 capable of irradiating the ion beam I to the
sample M arranged at the sample base 2. The sample base 2 is
arranged at an inner portion 4a of a vacuum chamber 4. The vacuum
chamber 4 is provided with a vacuum pump 5 and the inner portion 4a
can be exhausted to a high vacuum atmosphere. Further, the sample
base 2 is provided with a three axes stage 6 and the sample M can
be moved in Z direction constituting a direction of irradiating the
ion beam I, X direction and Y direction constituting two axes
substantially orthogonal to Z direction.
[0063] The ion beam lens-barrel 3 includes a cylinder member 8
formed with an irradiation port 7 communicated with the vacuum
chamber 4 at a front end thereof, and an ion source 9 constituting
a charged particle source contained on a base end side thereof at
an inner portion 8a of the cylinder member 8. An ion constituting
the ion source 9 is, for example, gallium ion (Ga.sup.+) or the
like. The ion source 9 is connected to an ion source control power
source 10. Further, by applying an acceleration voltage and an
extracting voltage by the ion source control power source 10, an
ion extracted from the ion source 9 can be accelerated to be
discharged as the ion beam I.
[0064] Further, at the inner portion 8a of the cylinder member 8, a
front end side of the ion source 9 is provided with a condenser
lens 11 and an object lens 12 as an optical system of focusing the
ion beam I emitted from the ion source 9. The condenser lens 11 and
the object lens 12 are adjusted such that respective center axes
thereof coincide with each other in a state of being substantially
in parallel with Z direction. The condenser lens 11 and the object
lens 12 are electrostatic lenses formed by 3 sheets of electrodes
formed with through holes 11a, 12a, and respectively connected to a
condenser lens control power source 13, an object lens control
power source 14. By applying a voltage to the condenser lens 11 by
the condenser lens control power source 13, the ion beam I passing
the through hole 11a and brought into a diverging state can be
focused. Further, by applying the voltage to the object lens 12 by
the object lens control power source 14, the ion beam I passing the
through hole 12a can further be focused to be irradiated to the
sample M as a focused ion beam.
[0065] Further, a movable aperture 15, a stigma 16, and a scanning
electrode 17 constituting scanning means are provided successively
from the base end side between the condenser lens 11 and the object
lens 12. The movable aperture 15 includes an aperture 18
constituting a through hole having a predetermined diameter, and an
aperture driving portion 19 of moving the aperture 18 in X
direction and Y direction. The aperture 18 narrows the ion beam I
irradiated from the condenser lens 11 in accordance with a diameter
of its own. Although according to the embodiment, only a single one
of the aperture 18 is provided, there may be constructed a
constitution having a plurality thereof by making the diameters
thereof different from each other and capable of selecting the
aperture of a preferable diameter by moving the aperture by the
aperture driving portion 19. Further, the stigma 16 is for
correcting astigmatism of the passing ion beam I, which is carried
out by applying a voltage from a stigma control power source 20.
Further, the scanning electrode 17 can deflect the passing ion beam
I in X direction and Y direction by a predetermined amount,
thereby, the ion beam I can be scanned on the sample M, or an
irradiating position can be shifted to irradiate to a predetermined
position.
[0066] Further, the ion source control power source 10, the
condenser lens control power source 13, the object lens control
power source 14, the stigma control power source 20, and the
scanning electrode control power source 21 described above are
connected to the control portion 30. That is, by controlling the
respective power sources by the control portion 30, the ion beam I
of a predetermined acceleration voltage and current can be focused
to irradiate to a predetermined position of the sample M. Further,
the control portion 30 is connected with a terminal 25, and the ion
beam I can be irradiated to the sample M also by setting various
conditions by the terminal 25. Further, the aperture driving
portion 19 and the three axes stage 6 are also connected to the
control portion 30, and the aperture 18 can be adjusted, further,
the position of the sample M can be adjusted under control by the
control portion 30. Further, the focused ion beam apparatus 1 is
provided with a secondary electron detector 22 capable of detecting
a secondary electron generated from the sample M when the ion beam
I is irradiated to the sample M, and a result of detection can be
outputted to image processing means 31 of the control portion 30.
The image processing means 31 can acquire a state of a surface of
the sample M as an image from the result of detection, that is,
observing means 32 is constituted by the secondary electron
detector 22 and the image processing means 31. Further, image data
acquired by the observing means 32 can be monitored by the terminal
25.
[0067] Here, when a center axis of the object lens 12 and a center
axis of the aperture 18 are positionally shifted in X direction and
Y direction, dimming referred to as off-axis aberration is brought
about in the ion beam I. In a state of bringing about such an
off-axis aberration, the ion beam I cannot accurately be irradiated
to the predetermined position of the sample M. Therefore, the
control portion 30 is provided with spot pattern forming means 33,
analyzing means 34, and adjusting position determining means 35 in
order to automatically correct the off-axis aberration of
observing, working the sample M. An explanation will be given as
follows of a procedure of correcting the off-axis aberration by
adjusting the axis of the aperture 18 as well as details of
operations of respective constitutions of the control portion 30 in
reference to the flowchart of FIG. 2.
[0068] First, a previously prepared standard sample N is arranged
at the sample base 2 (step S1). The standard sample N may
preferably be constituted by a material capable of forming an
irradiation mark referred to as spot pattern on a surface thereof
by irradiating the ion beam I, and the standard sample N preferably
includes a flat face for adjusting the axis of the aperture 18.
Further, even when the spot pattern is formed on the surface of the
sample, so far as the spot pattern is acceptable in observation,
working, actually observed, worked sample M may constitute the
standard sample N.
[0069] Next, as spot pattern forming step S2, a plurality of the
spot patterns are formed by irradiating the ion beam I to a
plurality of portions of the surface N1 of the standard sample N.
First, the spot pattern forming means 33 of the control portion 30
forms a spot pattern P by irradiating the ion beam I at an
arbitrary position for a constant period of time at the surface N1
of the standard sample N (step S21). At this occasion., a focal
point position of the object lens 12 is brought into a state of
over focal point relative to the surface N1 of the standard sample
N, that is, a distance between the object lens 12 and the surface
N1 of the standard sample N is made to be longer than a focal
length. Further, a position of a center axis L18 of the aperture 18
in X direction and Y direction at this occasion is set as an
aperture initial position A0 (0, 0), further, an irradiation
position on the surface Ni of the standard sample N is set as an
initial irradiation position B0 (0, 0).
[0070] FIG. 3 schematically shows a behavior of irradiating the ion
beam I. In FIG. 3, as shown by a two-dotted chain line L', when a
center axis L15 of the aperture 15 coincide with a center axis L12
of the object lens 12, the ion beam I is irradiated in an
irradiation range substantially symmetrical with regard to the
center axis L12 of the object lens 12. On the other hand, in the
case of the aperture initial position A0 at which the center axis
L18 of the aperture 18 is brought into a state of staying to be
positionally shifted relative to the center axis L12 of the object
lens 12, owing to the state of over focal point, the ion beam I is
irradiated to the initial irradiation position B0 in a direction
the same as that of the positional shift and eccentric to an
opposed side by interposing a focal point position F, and the
standard sample N is etched to form the spot pattern P in a range
constituting a geometrical center by the initial irradiation
position B0.
[0071] FIG. 4(a) shows an image when the spot pattern P is observed
by the observing means 32, and FIG. 4(b) is a sectional view broken
by A-A section of FIG. 4(a). As shown by FIGS. 4 (a), (b), in the
irradiation range of the surface N1 of the standard sample N, a
recess is formed by being etched by the ion beam I, the recess is
recognized on the image as the spot pattern P. That is, the recess
is recognized as a halo P1 substantially in a shape of a circle an
outer edge of which is constituted by start of the recess of the
surface N1, and the initial irradiation position B0 substantially
coincides with a geometrical center P3 of the halo P1. Further, as
shown by FIG. 4(b), the spot pattern P shows a sectional shape in
which a depth of the recess is deepened rapidly as proceeding to an
inner portion. Therefore, as shown by FIG. 4(a), the acquiring
image is formed with a gradation substantially in a circular shape
in accordance with the depth of the recess at the inner portion of
the halo P1, and a spot center P2 is formed at a center thereof.
The spot center P2 shows the most deeply etched position. At a
vicinity of the spot center P2, the recess is deepened rapidly, and
therefore, almost all of the secondary electrons discharged emitted
from the vicinity is not detected by the secondary electron
detector 22 of the observing means 32. Therefore, in the acquired
image, the spot center P2 is recognized as a black point. Here, by
positionally shifting the center axis L18 of the aperture 18
relative to the center axis L12 of the object lens 12, the spot
center P2 is formed to be positionally shifted relative to the
geometrical center P3 of the halo P1. Further, the positionally
shifted direction corresponds to a direction of positionally
shifting the center axis L18 of the aperture 18 relative to the
center axis 12 of the object lens 12.
[0072] When the initial spot pattern P is formed in this way, a
next spot pattern Q is further formed. First, the spot pattern
forming means 33 of the control portion 30 moves the aperture 18 to
an aperture position A1 (.DELTA.X1, .DELTA.Y1) moved from the
aperture initial position A0 (0, 0) by a moving amount .DELTA.X1 in
X direction and a moving amount .DELTA.Y1 in Y direction which are
previously set (step S22). Further, the spot pattern forming means
33 shifts the ion beam I by moving amounts .alpha..DELTA.X1,
.alpha..DELTA.Y1 of amounts of the moving amounts .DELTA.X1,
.DELTA.Y1 of the aperture 18 multiplied by a previously set
constant .alpha. by the scanning electrode control power source 21
and the scanning electrode 17 (step S23). Further, a second portion
of the spot pattern Q is formed by irradiating the ion beam I to
the standard sample N by a constant period of time under the state
(step S24).
[0073] When the spot patterns P, Q are finished to form on the
surface N1 of the standard sample N in this way, an image of the
surface N1 of the standard sample N is acquired by the observing
means 32 (step S3). That is, the control portion 30 irradiates the
ion beam I from the ion source 9 by setting the acceleration
voltage to be low by the ion source control power source to scan
over a total of the surface N1 of the standard sample N by the
scanning electrode 17. Further, secondary electrons emitted from
the surface N1 of the standard sample N in accordance with the
irradiation are successively detected by the secondary electron
detector 22 of the observing means 32, a result thereof is formed
into an image by the image processing means 31, thereby, the image
of the surface N of the standard sample N can be acquired. FIG. 5
shows the acquired image.
[0074] Next, as spot pattern analyzing step S4, the formed spot
patterns P, Q are analyzed from the acquired image. First, the
analyzing means 34 of the control portion 30 processes to binarize
the acquired image to form binarized data (step S41). Thereby,
whereas the surface N1 of the standard sample N which is not formed
with the spot patterns P, Q becomes black color, the inner portions
of the spot patterns P, Q become white color, and the halos P1, Q1
can clearly be identified by contrast. Further, the spot centers
P2, Q2 of the spot patterns P, Q become black color and can clearly
be identified from other portions of the spot patterns P, Q.
[0075] Next, as shown by FIG. 5, based on the binarized data of the
image, positions of the centers P3, Q3 of the halos P1, Q1 and the
positions of the spot centers P2, Q2 of the respective spot
patterns P, Q are calculated (S42). That is, first, from the
recognized halo P1, the position of the geometrical center P3 is
calculated at a first portion of the spot pattern P, and the
position is made to constitute the initial irradiation position B0
(0, 0). Further, by constituting a reference by the initial
irradiation position B0 (0, 0), a position C0 (Xc0, Yc0) of the
spot center P2 of the spot pattern P is calculated. Further, by
constituting a reference by the initial irradiation position B0 (0,
0), the irradiation position B1 (Xb1, Yb1) constituting a
geometrical center Q3 of a halo Q1 of a second portion of the spot
pattern Q and a position (Xc1, Yc1) of the spot pattern Q2 are
calculated.
[0076] Here, a relationship shown below is established between the
initial irradiation position B0 constituting an original point of
the first portion and the irradiation position portion B1 of the
second portion. As shown by FIG. 6, when the center axis L18 of the
aperture 18 is moved from the first portion of the aperture initial
position A0 to the second portion of the aperture position A1,
since the focal point position F is constant, the irradiation
position on the surface N1 of the standard sample N is displaced
from the initial irradiation position B0 to the irradiation
position B1'. The irradiation position B1' is represented by B1'
(.beta..DELTA.X1, .beta..DELTA.Y1) from a similarity relationship
constituting the reference by the focal point position F by using a
coefficient .beta. determined by the moving amounts .DELTA.X1,
.DELTA.Y1 of the aperture 18 and a position relationship of the
focal point position F and the standard sample N. That is, as shown
by FIG. 5, a component Xb1 in X direction of the irradiation
position B1 irradiated with the ion beam I as the second portion is
represented by Xb1=(.alpha.+.beta.).DELTA.X1 from the moving amount
of the aperture 18 and the shift amount of the ion beam I.
Similarly, a component Yb1 in Y direction is represented by
Yb1=(.alpha.+.beta.) .DELTA.Y1, that is, the position of the center
axis L18 of the aperture 18 and the irradiation position on the
surface N1 of the standard sample N are provided with a similarity
relationship of a similarity ratio (.alpha.+.beta.).
[0077] Next, as the adjusting position determining step S5, an
adjusting position T capable of making the center axis L18 of the
aperture 18 coincide with the center axis L12 of the object lens 12
is calculated. As shown by FIG. 5, the adjusting position
determining means 35 of the control portion 30 calculates an
intersection D (Xd, Yd) of a linear line Lp connecting the center
P3 of the halo P1 and the spot center P2 of the spot pattern P and
a linear line Lq of connecting the center Q3 of the halo Q1 and the
spot center Q2 of the spot pattern Q based on a calculation result
of spot pattern analyzing step S4 (step S51). Next, based on the
calculated intersection D, an adjusting position T (Xt, Yt) of the
center axis L18 of the aperture 18 constituting the reference by
the aperture initial position AO is calculated.
[0078] Here, as described above, the spot center P2 is formed by
being positionally shifted in a direction in correspondence with a
direction of positionally shifting the center axis L18 of the
aperture 18. Therefore, a direction of adjusting the center axis
L18 of the aperture 18 relative to the aperture initial position A0
coincides with a direction of the liner line Lp in correspondence
therewith. Similarly, a direction of adjusting the center axis L18
of the aperture relative to the aperture position A1 in
correspondence with the spot pattern Q coincides with a direction
of the linear line Lq in correspondence therewith. Therefore, a
component Xt in X direction of the adjusting position T becomes a
value of the component Xd in X direction of the intersection D
divided by the similarity ratio (.alpha.+.beta.) and is calculated
by Xt=Xd/(.alpha.+.beta.). Similarly, a component Yt in Y direction
of the adjusting position T becomes a value of the component Yd in
Y direction of the intersection D divided by the similarity ratio
(.alpha.+.beta.) and is calculated by Yt=Yd/(.alpha.+.beta.).
[0079] Finally, as center axis position adjusting step S6, the
control portion 30 moves the position of the center axis 18 of the
aperture 18 to a position constituting the adjusting position T
relative to the aperture initial position A0 by driving the
aperture driving portion 19. Thereby, the center axis L15 of the
aperture 18 is made to substantially coincide with the center axis
L12 of the lens 12 and the off-axis aberration can be
corrected.
[0080] As described above, by forming the plurality of spot
patterns P, Q by making the position of the center axis L18 of the
aperture 18 differ, the positional shift of the aperture 18 can
quantitatively be evaluated and automatically adjusted, and easy
and accurate adjustment can be realized in a short period of time.
Further, although according to the embodiment, an explanation has
been given such that fine adjustment is automatically carried out
by the control portion 30, adjustment of the position of the center
axis of the aperture can easily and accurately be carried out in a
short period of time by the procedure even when the adjustment is
carried out by a manual operation. Further, the aperture driving
portion 19 and the scanning electrode 17 may be operated by a
manual operation such that the center of the halo of the spot
pattern is made to coincide with the position constituting the
intersection D while confirming the image acquired in real
time.
[0081] Further, although according to the embodiment, when the next
spot pattern is formed, the aperture 18 is moved and the ion beam I
is shifted by the scanning electrode 17, the adjustment can be
carried out by a similar method even when only the aperture 18 is
moved. However, by shifting the ion beam I by the scanning
electrode 17, a plurality of formed spot patterns can be formed not
to overlap each other. Therefore, the spot pattern can further
clearly be identified from the acquired image and further accurate
axis adjustment can be carried out. Further, although the scanning
electrode 17 is provided as the scanning means and the ion beam I
is shifted by the scanning electrode 17, the side of the sample M
may be moved in X direction and Y direction by the three axes stage
6 in place thereof. A similar effect can be achieved so far as at
least the irradiation position of the ion beam I can be moved
relative to the sample M. Further, although at the spot pattern
forming step S2, the ion beam I is brought into a state of over
focal point, the embodiment is not limited thereto but the ion beam
I may be brought into a state of under focal point. Although there
may be constituted a focal point state in which at least a spot
pattern of a constant size which can be identified is formed, by
bringing about a state of over focal point as in the embodiment,
the identification can be facilitated by adjusting to a larger spot
pattern.
[0082] Further, although according to the embodiment, the adjusting
position is calculated by forming two portions of the spot
patterns, the embodiment is not limited thereto. For example, four
portions thereof may be formed. In this case, as shown by FIG. 7,
the adjusting position T is calculated from an intersection E of
respective linear lines Lo, Lp, Lq, Lr of four spot patterns O, P,
Q, R, when the intersection is not carried out at one point by an
error or the like, by averaging the intersections, an accuracy can
be promoted more than when the intersection is calculated by two
portions of the spot patterns. Further, the embodiment is not
limited to the axis adjustment of the aperture by carrying out the
above-described step only by one time but the step may be repeated
by a plurality of times. Thereby, the adjustment can efficiently be
carried out and an adjustment accuracy can be promoted by carrying
out the adjustment by reducing the magnification of the image by
the observing means at a first time, and carrying out the
adjustment by increasing the magnification at a second time or
thereafter.
Second Embodiment
[0083] FIG. 8 shows a second embodiment according to the invention.
According to the embodiment, members common to member used in the
above-described embodiment are attached with the same notations and
an explanation thereof will be omitted.
[0084] As shown by FIG. 8, a focused ion beam apparatus 40 of the
embodiment includes an SEM lens-barrel 42 as observing means 41.
According to the embodiment, by using the SEM lens-barrel 42 and
the secondary electron detector 22 as means for acquiring the image
used in the analyzing step, the axis adjustment of the aperture 18
can be carried out based on a further accurate image. Further, the
axis adjustment of the aperture, not illustrated, can be carried
out by a similar method not only by the adjustment of the ion beam
lens-barrel 3 but the SEM lens-barrel 42.
Third Embodiment
[0085] FIG. 9 shows a second embodiment according to the invention.
According to the embodiment, members common to members used in the
above-described embodiments are attached with the same notations
and an explanation thereof will be omitted.
[0086] As shown by FIG. 9, a focused ion beam apparatus 50 of the
embodiment further includes a rare gas ion beam lens-barrel 51. The
rare gas ion beam lens-barrel 51 can irradiate a rare gas ion of,
for example, argon ion or the like as an ion beam at a low
acceleration, can work a sample without damaging the sample, and is
preferably used in finishing of working by a normal ion beam. Even
in such a focused ion beam apparatus 50, the axis adjustment of the
aperture, not illustrated, of not only the ion beam lens-barrel 3
but also the SEM lens-barrel 42 or the rare gas ion beam
lens-barrel 51 can be carried out by a similar method.
Fourth Embodiment
[0087] FIG. 10 and FIG. 11 show a second embodiment according to
the invention. According to the embodiment, members common to
members used in the above-described embodiments are attached with
the same notations and an explanation thereof will be omitted.
[0088] As shown by FIG. 10, a focused ion beam apparatus 60 of the
embodiment further includes a gas introducing mechanism 61. In the
focused ion beam apparatus 60, deposition can be carried out by
introducing an organic gas to the surface of the sample by the gas
introducing mechanism 61. Therefore, according to the focused ion
beam apparatus 60 of the embodiment, at the spot pattern forming
step, the spot pattern is not formed by etching the sample but the
spot pattern may be formed by deposition. That is, by introducing
an organic gas G by the gas introducing mechanism 61 and
irradiating the ion beam I, a spot pattern P' in a projected shape
as shown by FIG. 11 is formed at an irradiation position. Even in
the spot pattern P' in the projected shape, the axis adjustment of
the aperture can be carried out similarly based on the spot pattern
P' by enabling to identify the spot pattern P' from the acquired
image by the observing means.
[0089] Although the embodiments of the invention have been
described in details in reference to the drawings as described
above, the specific constitution is not limited to the embodiments
but includes also a design change or the like within the range not
deviated from the gist of the invention.
[0090] Further, although as the charged particle beam apparatus,
the focused ion beam apparatus are pointed out as examples in the
respective embodiments, the charged particle beam apparatus are not
limited thereto. For example, an ion beam exposure apparatus or the
like is pointed out as the apparatus using an ion beam as a charged
particle beam similarly. Further, as apparatus of using an electron
beam as a charged particle beam, a scanning electron microscope, an
electron beam exposure apparatus or the like is pointed out. Also
in the apparatus, by providing a similar constitution as a control
portion, the axis of the aperture included therein can easily and
accurately be adjusted automatically in a short period of time.
Further, although as the standard sample, the standard sample
capable of forming the spot pattern by etching or deposition is
selected, otherwise, a resist film or the like is selected. In this
case, by irradiating a charged particle beam to a resist film
constituting a standard sample to expose, a similar adjustment can
be carried out by an exposure pattern.
INDUSTRIAL APPLICABILITY
[0091] According to the charged particle beam apparatus of the
invention, by only providing the spot pattern forming means, the
analyzing means., the adjusting position determining means as the
control portion and forming the plurality of spot patterns on the
sample, the position of the center axis of the aperture can be
adjusted automatically, easily and accurately in a short period of
time. Therefore, by the simple and accurate adjustment of the
position of the center axis of the aperture, accurate observation
without dimming can be carried out and accurate working can be
carried out.
* * * * *